Government imposed requirements for fuel economy and emissions reduction are one reason fuel systems manufacturers seek to provide precise control over the amount of fuel that is injected during injection events of a combustion cycle. More specifically, a goal of many high pressure fuel injection systems is to provide increased control of the amount of fuel injected by the fuel injectors of an internal combustion engine.
As shown in FIG. 1, a typical high pressure fuel pump system 10 generally includes a fuel supply 12 which supplies fuel to a hydro mechanical actuator such as an inlet metering valve 14. Metering valve 14, which is controlled by an electronic control module (“ECM”) 15, is configured to control the amount of fuel provided to a plurality of high pressure pumping chambers 16. Pumping chambers 16 then disperse the fuel to a receptacle such as a common rail fuel apparatus or accumulator 18.
In many such systems, metering valve 14 includes a variable area orifice operated by a solenoid. In certain embodiments, the linear position of a spool inside metering valve 14 controls the amount of fuel to be supplied to pumping chambers 16. As such, metering valve 14 may be configured to prevent fuel from passing to chambers 16 when metering valve 14 is fully closed. However, in many systems, the mechanical configuration of metering valve 14 is insufficient to completely prevent fuel flow, and some leakage occurs. Moreover, in some systems the pressure of the fuel supply 12 to metering valve 14 requires significant counter-force by valve 14 when valve 14 is moved to a partially opened position to maintain valve 14 in its desired position. Generally, this counter-force is provided by a high performance solenoid controlled by ECM 15. Finally, in order to deliver the fuel economy and emission reduction desired, it is desirable to provide a highly accurate mechanism for metering fuel to chambers 16 when valve 14 is opened.